The present invention concerns a switch device for verifying the fastening of an automobile seatbelt lock with at least two switch elements whose switch condition can be determined, as well as a control component that can be moved in the seatbelt lock and through which the switch condition of the switch elements can be changed.
A generic switch device is known from, for example, DE 43 27 989. It discloses a buckle detection device that is positioned on the seatbelt of an automobile and which has two parallel guide arms in which resistors of various sizes are positioned. In the ends of the two guide arms there are changeover switches that are directly or indirectly moved mechanically when the belt tongue is inserted into and removed from the seatbelt lock and thereby release one or the other guide arm. Depending on whether the seatbelt tongue is inserted into the belt lock, the guide arm with the larger or the smaller of the resistors is activated, which activation can be determined by means of an appropriate resistance, tension, or current measurement. The monitoring of the mechanical function of the switch is achieved by the fact that the entire circuit is controlled in such manner that an undesired line break is determined when one of the switches locks in one position and thus cannot be moved. In this case neither of the guide arms is released, which leads to an undesired situation that can be determined in an evaluation component. By means of the evaluation component an error function of this type can lead to the transmitting of an appropriate signal for the user. It is likewise possible that in the presence of an error function or an unfastened condition of the seatbelt, a threshold value for a delay in the release of, for example, an airbag or a belt tightener in the event of occurrence of an accident can be appropriately lowered.
A similar arrangement is described in U.S. Pat. No. 5,590,904. The belt lock disclosed therein has a switch that can be opened by sliding the belt tongue into the belt lock. A resulting change in the resistance of a connected circuit is detected by an evaluation component that is connected with the safety equipment of the vehicle, for example an airbag or a belt tightener, and which controls their response in the event of a delay caused by an accident depending on the switch condition of the belt lock. DE 43 08 038 discloses a switch device for a belt lock in which the switch position can be changed by means of a permanent magnet and a ferromagnetic ground positioned in the area of the magnet. The ferromagnetic ground is located on a stationary contact spring element in a housing, which said element can be connected with one of two stationary contacts, depending on its position. The position of the contact spring element and hence a switch position is determined by the position of the permanent magnets, which said position depends on whether the belt tongue is properly gripped in the belt lock.
The disadvantage in the previously known switch devices is that mechanically operated switches are always used, which diminishes the reliability and security of the switch device.
It is the task of this invention to develop a generic switch device in such manner that its reliability is increased.
This task is performed by starting with a generic switch device, switch elements designed as sensors, and the switch condition of the switch elements changeable by means of an interaction between control element and sensors. In this way it is possible to create a reliable switch device in which the switch conditions are defined not by mechanically adjustable switches but by sensors whose switch condition can be changed by an interaction between the control element and the sensors. In this way disadvantages occurring for example with a locking of a mechanical switch in one position or with the corrosion or dirtying of switch points can be securely prevented.
It is particularly advantageous if the control element and the sensors are designed in such manner that a contact-free interaction between the control element and the sensors can be created. Such an embodiment of this invention leads to a situation in which there is no need for mechanical contact for the creation of signals indicating if the belt tongue is properly gripped in the belt lock. A contact-free interaction between the control element and the sensor is possible by means of, for example, a magnetic field. In contrast to mechanically activated switches, contact-free interaction facilitates reliable operation of the switch device even when manufacturing tolerances in the manufacturing of mechanical switches influence their functioning. Contact-free interaction between the control element and the sensor thus creates a situation in which neither the activation of the sensor itself nor a change in the switch status of the sensor is caused by a mechanical activation of an appropriate construction element. Instead, mechanical components can be eliminated, which facilitates high operating security even if dirt or manufacturing tolerances are to be expected.
In a preferred embodiment of the within invention, two sensors are permanently positioned in the belt lock or in the lock casing. The providing of two sensors increases operating security in that in the event one of the sensors fails there is no unintentional assumption that the switch device is functioning properly, since the switch signal of the functioning sensor can be brought in as an additional aide to evaluating the switch condition or error function. The sensors can also be connected with a similarly advantageous permanent evaluation unit that depending on the signals or the switch conditions of the sensors reports an error or a switch situation showing that the belt is or is not fastened.
According to a preferred embodiment of the present invention, the sensors are designed as Hall probes. Such Hall probes serve as contact-free signal generators in which a tension dependent on a magnetic field can be probed.
The control element can include a magnet, preferably a permanent magnet, positioned in such manner that an interaction can be created between the magnets and the sensors designed, for example, as Hall probes. Such an arrangement of a control element with a magnet is relatively simple to manufacture, since the control element need only be positioned near the permanently positioned sensors or Hall probes and be equipped with a permanent magnet in an appropriately adjacent area. The magnets chosen must be of such size that only one of the sensors or only one of the Hall probes is appropriately acted on by a magnetic field. The presence of the magnet near one of the sensors/Hall probes leads to generation of a specific pre-programmable switch condition that is clearly dependent on a specific position of the control element and hence the position of the belt lock tongue in the belt lock. A major advantage of such an arrangement is that the electronic device consisting of sensors or Hall probes and evaluation unit can be completely sealed against external influences, since a mechanical contact between the control element and the sensor is as unnecessary as a mechanically activated switch. In the within case it is sufficient if the sensors or Hall probes are positioned in an area adjacent to the control element in different positions or to the permanent magnets installed on them.
It is particularly advantageous if the belt tongue can be fixed in the belt lock with a locking pin and the locking pink contains the control element. This guaranties optimum mechanical operating security of the entire switch device. Since the position of the locking pin can be directly determined by means of the permanent magnet or the probes, an error function can be reliably prevented by an indirect and error-affected determination of the positions of the locking pin and the control element. If the belt tongue is properly inserted into the belt lock, according to the invention the locking pin is also in a predetermined position. This position can then be correctly determined through the interaction between the control element and the sensors.
In a preferred embodiment of the present invention a form is provided to hold the sensors and the evaluation unit. The effect of such a form is to prevent the sensors from collecting dirt or being damaged by outside influences.
In a preferred embodiment of the present invention a control unit and an evaluation unit can be linked so that in the control unit the output signal of the evaluation unit can be transformed into a threshold or an error value. If because of the switch circumstances of the sensors it is determined in the evaluation unit that the belt tongue is not properly inserted in the belt lock, an appropriate signal can be transmitted to the control unit. The control unit can transform this signal into a threshold value that for example can determine delay in an accident in which an airbag is supposed to be released. If the belt is not fastened, or if the switch device is malfunctioning, this threshold value is lower than when the belt is properly fastened.
It is particularly advantageous if the control unit and the evaluation unit can be combined in one unit. If in addition the sensors according to the invention are located in this unit, the entire electronic device can be combined into a single compact structural component and if necessary can be protected against outside influences.
In a preferred embodiment of the present invention the control element is positioned on the belt lock tongue so that the position of the control element is changed by a movement of the belt lock tongue.